In the case of an agricultural boom-type sprayer there arises in certain types of sprayer a requirement to fold the boom portions inwardly and upwardly for transport purposes. Various mechanisms and linkages have been proposed for this purpose and a preferred arrangement is one in which a single actuator such as a ram can cause simultaneous relative pivotal movement of two or more boom portions so that they effect the required folding movement in a progressive manner. In such a relatively complex assembly, it will be appreciated that requirements arise for adjustment of the mechanism so that the boom portions revert to their required horizontal positions when required and that they do so in a reliable manner without becoming out of adjustment due to wear, and without a tendency to oscillate or vibrate during use.
Various complex proposals have been made in this regard including the use of planetary geared mechanisms interconnecting the boom portions, but such arrangements are vulnerable to overload and do not provide the necessary rugged durability which is somewhat of a prerequisite for day-to-day farm usage.
References disclosing general background and other technical subject matter related to the present invention are as follows
US 42 13 565 (Jackson) PA1 GB 15 92 859A (Haylock) PA1 GB 20 26 828A (Clark Equipment) PA1 GB 21 10 062A (Moteska) PA1 GB 21 49 281A (Moteska)
These disclosures include (Clark Equipment, FIG. 2) the use of a hydraulic shock absorber 124 that serves as a damping means with respect to actuation of the boom of a mobile vehicle under the control of a mechanical linkage 80 that serves as a forcing means for selectively applying an actuating force to move the boom between its upper and lower positions. The hydraulic shock absorber 124 acts in parallel with a spring 58 in a manner comparable to that in an automotive suspension in the sense that the shock absorber serves to damp movement permitted by spring 58. The actual movement is caused by linkage 80.
Jackson, (FIG. 2) proposes to use a spring to provide "shock absorbing" characteristics. Haylock, (FIG. 3) proposes a somewhat similar spring-biased ram control linkage. Moteska, (FIG. 2) proposes a twin-compression-spring "damper" connected in series with a hydraulic ram to pivot a boom portion to and from its forwardly-folded transport position in a mobile spraying machine.
None of the above-cited references proposes the use of an oil-damped extensible and retractable hydraulic shock-absorbing strut member to apply to a movable implement portion the necessary forces to effect movement of such implement portion between its working and stowed or other positions during use. Indeed, none of the references uses an oil-damped extensible and retractable hydraulic shock-absorbing strut member in any way as a means for moving an implement portion in any way whatever. The only disclosure of use of a hydraulic shock absorber in the above references is in the Clark Equipment specification, and that utilises the linkage 80 to apply control forces to the boom. The shock-absorber 124 is used solely to damp boom movement thereby caused.
Accordingly, none of the above specifications teaches the use of a hydraulic shock absorbing strut member to control a pivotable boom portion in order to achieve the advantages disclosed herein including improved control, automatic strut length-adjustment, yielding under load and related dynamic advantages. Indeed, the concept of using as a thrust-transmitting strut member a mechanical construction which actually passively yields under compressive or extensive loads is apparently one which has hitherto been avoided presumably as a result of a prejudice against the lack of controllability which may hitherto have been perceived in such an arrangement.
References in the prior art to "damping means" such as item (8) in the Moteska specification refer (apart from the above-discussed disclosure in the Clark Equipment specification) to the use of spring systems, whether double or single acting. Although such use of the term damping means may be in accordance with common parlance, spring systems do not provide, in principle, operating characteristics which are strictly damped since (ignoring friction) spring systems merely sequentially store and then release energy received and do not offer the energy-absorbing damping function which a hydraulic damper offers by virtue of its orifice-and-piston-based damping function.